N-functionalized imidazole-containing systems and methods of use

ABSTRACT

Systems containing imidazoles or blends of imidazoles and amines are described herein. Methods of their preparation and use are also described herein. The methods of using the systems include the reduction of volatile compounds from gas streams and liquid streams.

CROSS-REFERENCE TO PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.13/430,813, filed on Mar. 27, 2012, which claims the benefit of priorityto U.S. Provisional Application No. 61/468,314, filed Mar. 28, 2011,both of which are incorporated herein by reference in their entireties.

FIELD

The subject matter disclosed herein generally relates to systemscontaining imidazoles or imidazole-amine blends and methods of theirpreparation. Also, the subject matter described herein generally relatesto methods of using the systems described herein to capture and reducevolatile compounds from gas streams and liquid streams.

BACKGROUND

There is a worldwide interest in capturing and sequestering or reusingcarbon dioxide (CO₂) emissions to stabilize the climate. Aqueous amineprocesses, widely used throughout the natural gas industry to reduce CO₂from gas streams via chemical reaction, represent the benchmark by whichCO₂ capture technologies are evaluated (NETL, Carbon SequestrationTechnology Roadmap and Program Plan (2007); Rochelle, G. T., “AmineScrubbing for CO₂ Capture,” Science, 325:1652-1654 (2009)). Whileeffective at reducing CO₂ from gas streams, amine processes are highlyenergy intensive, with much of the energy penalty attributed to boilingwater during amine regeneration. Thus, aqueous amine processes willinherently suffer from large energy penalties. However, new solventswith little or no volatility can provide the desired energy efficiency.

Ionic liquids have received significant attention as solvents for CO₂capture (Bara, J. E., et al., “Guide to CO₂ Separations inImidazolium-based Room-Temperature Ionic Liquids,” Ind. Eng. Chem. Res.,48:2739-2751 (2009)). As ionic liquids do not evaporate, theypotentially offer greatly improved energy efficiency. However, the useof ionic liquids for CO₂ capture has not been scaled due to limitationsof their physical and thermodynamic properties. Issues with ionicliquids consistently cited are very low CO₂ loading, high viscosity, andexceedingly high costs (NETL, Existing Plants, Emissions andCapture—Setting CO ₂ Program Goals, DOE/NETL-2009/1366). Inclusion ofamine functionalities within the ionic liquid (i.e., “task-specific”ionic liquids) or blending ionic liquids with commodity amines such asmonoethanolamine (MEA) greatly improves the CO₂ capacity of the solventand also reduces the energy requirement (NETL, Existing Plants,Emissions and Capture—Setting CO ₂ Program Goals, DOE/NETL-2009/1366;Camper, D. et al., “Room-Temperature Ionic Liquid—Amine Solutions:Tunable Solvents for Efficient and Reversible Capture of CO₂ ,” Ind.Eng. Chem. Res., 47:8496-8498 (2008)). While using ionic liquid-amineblends is promising, alternative volatile solvents that overcome theviscosity and cost limitations of ionic liquids are needed.

SUMMARY

In accordance with the purposes of the disclosed materials, compounds,compositions, and methods, as embodied and broadly described herein, thedisclosed subject matter, in one aspect, relates to compounds andcompositions and methods for preparing and using such compounds andcompositions. In a further aspect, the disclosed subject matter relatesto systems that can be used for the capture of volatile compounds inindustrial and commercial natural gas production and power generationindustries. More specifically, systems for the reduction of volatilecompounds are described herein. The system comprises an N-functionalizedimidazole and can optionally include an amine. The N-functionalizedimidazole for use in the disclosed system is non-ionic under neutralconditions (e.g., under conditions where an acidic proton is notavailable). In other examples, the N-functionalized imidazole is notfunctionalized on both nitrogen atoms.

Further provided herein are methods for reducing CO₂, SO₂, or H₂S from astream (e.g., a gas stream or a liquid stream). The methods includecontacting the stream with an effective amount of a system comprising anN-functionalized imidazole and, optionally, an amine, wherein theN-functionalized imidazole is non-ionic under neutral conditions.

Methods for sweetening a natural gas feed stream are also providedherein. The methods comprise contacting the natural gas feed stream withan effective amount of a system as described herein to form a purifiednatural gas feed stream and a gas rich system and separating thepurified natural gas feed stream from the gas-rich system. The methodscan further comprise regenerating the system by, for example, heating orpressurizing the gas rich system.

Additional advantages will be set forth in part in the description thatfollows, and in part will be obvious from the description, or may belearned by practice of the aspects described below. The advantagesdescribed below will be realized and attained by means of the elementsand combinations particularly pointed out in the appended claims. It isto be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive.

DESCRIPTION OF FIGURES

The accompanying Figures, which are incorporated in and constitute apart of this specification, illustrate several aspects of the inventionand together with the description serve to explain the principles of theinvention.

FIG. 1 is a schematic of the gas solubility apparatus.

FIG. 2 is a graph depicting the relationship between CO₂ partialpressure and loading per initial amine molecule in 80:20 (v/v)1-butylimidazole-amine mixtures at 25° C.

FIG. 3 is a graph depicting the relationship between CO₂ partialpressure and loading in 80:20 (v/v)1-butylimidazole+N-methylethanolamine (NMEA) mixtures at temperaturesbetween 25-80° C.

DETAILED DESCRIPTION

The materials, compounds, compositions, articles, and methods describedherein may be understood more readily by reference to the followingdetailed description of specific aspects of the disclosed subject matterand the Examples included therein.

Before the present materials, compounds, compositions, kits, and methodsare disclosed and described, it is to be understood that the aspectsdescribed below are not limited to specific synthetic methods orspecific reagents, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular aspects only and is not intended to be limiting.

Also, throughout this specification, various publications arereferenced. The disclosures of these publications in their entiretiesare hereby incorporated by reference into this application in order tomore fully describe the state of the art to which the disclosed matterpertains. The references disclosed are also individually andspecifically incorporated by reference herein for the material containedin them that is discussed in the sentence in which the reference isrelied upon.

A. General Definitions

In this specification and in the claims that follow, reference will bemade to a number of terms, which shall be defined to have the followingmeanings:

Throughout the description and claims of this specification the word“comprise” and other forms of the word, such as “comprising” and“comprises,” means including but not limited to, and is not intended toexclude, for example, other additives, components, integers, or steps.

As used in the description and the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a composition”includes mixtures of two or more such compositions, reference to “thecompound” includes mixtures of two or more such compounds, and the like.

“Optional” or “optionally” means that the subsequently described eventor circumstance can or cannot occur, and that the description includesinstances where the event or circumstance occurs and instances where itdoes not.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another aspect includes from the one particular value and/orto the other particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint. It is also understood that there are a number of valuesdisclosed herein, and that each value is also herein disclosed as“about” that particular value in addition to the value itself. Forexample, if the value “10” is disclosed, then “about 10” is alsodisclosed. It is also understood that when a value is disclosed, then“less than or equal to” the value, “greater than or equal to the value,”and possible ranges between values are also disclosed, as appropriatelyunderstood by the skilled artisan. For example, if the value “10” isdisclosed, then “less than or equal to 10” as well as “greater than orequal to 10” is also disclosed. It is also understood that throughoutthe application data are provided in a number of different formats andthat this data represent endpoints and starting points and ranges forany combination of the data points. For example, if a particular datapoint “10” and a particular data point “15” are disclosed, it isunderstood that greater than, greater than or equal to, less than, lessthan or equal to, and equal to 10 and 15 are considered disclosed aswell as between 10 and 15. It is also understood that each unit betweentwo particular units are also disclosed. For example, if 10 and 15 aredisclosed, then 11, 12, 13, and 14 are also disclosed.

By “reduce” or other forms of the word, such as “reducing” or“reduction,” is meant lowering of an event or characteristic (e.g.,volatile compounds in a stream). It is understood that this is typicallyin relation to some standard or expected value, in other words it isrelative, but that it is not always necessary for the standard orrelative value to be referred to. For example, “reduces CO₂” meansreducing the amount of CO₂ in a stream relative to a standard or acontrol. As used herein, reduce can include complete removal. In thedisclosed method, reduction can refer to a 10%, 20%, 30%, 40%, 50%, 60%,70%, 80%, 90%, or 100% decrease as compared to the standard or acontrol. It is understood that the terms “sequester,” “capture,”“remove,” and “separation” are used synonymously with the term “reduce.”

By “treat” or other forms of the word, such as “treated” or “treatment,”is meant to add or mix two or more compounds, compositions, or materialsunder appropriate conditions to produce a desired product or effect(e.g., to reduce or eliminate a particular characteristic or event suchas CO₂ reduction). The terms “contact” and “react” are used synonymouslywith the term “treat.”

It is understood that throughout this specification the identifiers“first” and “second” are used solely to aid in distinguishing thevarious components and steps of the disclosed subject matter. Theidentifiers “first” and “second” are not intended to imply anyparticular order, amount, preference, or importance to the components orsteps modified by these terms.

B. Chemical Definitions

References in the specification and concluding claims to parts by weightof a particular element or component in a composition denotes the weightrelationship between the element or component and any other elements orcomponents in the composition or article for which a part by weight isexpressed. Thus, in a compound containing 2 parts by weight of componentX and 5 parts by weight component Y, X and Y are present at a weightratio of 2:5, and are present in such ratio regardless of whetheradditional components are contained in the compound.

A weight percent (wt. %) of a component, unless specifically stated tothe contrary, is based on the total weight of the formulation orcomposition in which the component is included.

The term “ion,” as used herein, refers to any molecule, portion of amolecule, cluster of molecules, molecular complex, moiety, or atom thatcontains a charge (positive, negative, or both at the same time withinone molecule, cluster of molecules, molecular complex, or moiety (e.g.,Zwitterions)).

The term “anion” is a type of ion and is included within the meaning ofthe term “ion.” An “anion” is any molecule, portion of a molecule (e.g.,Zwitterion), cluster of molecules, molecular complex, moiety, or atomthat contains a net negative charge.

The term “cation” is a type of ion and is included within the meaning ofthe term “ion.” A “cation” is any molecule, portion of a molecule (e.g.,Zwitterion), cluster of molecules, molecular complex, moiety, or atomthat contains a net positive charge.

The term “non-ionic” as used herein refers to being free of ionic groupsor groups that are readily substantially ionized in water. A “non-ionic”compound does not contain a charge at neutral pH (e.g., at a pH from 6.7to 7.3). However, non-ionic compounds can be made to have a charge underacidic or basic conditions or by methods known in the art, e.g.,protonation, deprotonation, oxidation, reduction, alkylation,acetylation, esterification, deesterification, hydrolysis, etc. Thus,the disclosed “non-ionic” compounds can become ionic under conditionswhere, for example, an acidic proton is available to protonate thecompound.

The term “volatile compound” as used herein refers to chemical compoundsthat are capable of vaporizing to a significant amount or that exist asa gas at ambient conditions. The “volatile compounds” described hereinare found in the streams and have higher vapor pressures than thestream, such as natural gas feeds. Examples of volatile compoundsinclude light gases and acid gases, such as CO₂, O₂, N₂, CH₄, H₂,hydrocarbons, H₂S, SO₂, NO, NO₂, COS, CS₂, and the like.

As used herein, the term “substituted” is contemplated to include allpermissible substituents of organic compounds. In a broad aspect, thepermissible substituents include acyclic and cyclic, branched andunbranched, carbocyclic and heterocyclic, and aromatic and nonaromaticsubstituents of organic compounds. Illustrative substituents include,for example, those described below. The permissible substituents can beone or more and the same or different for appropriate organic compounds.For purposes of this disclosure, the heteroatoms, such as nitrogen, canhave hydrogen substituents and/or any permissible substituents oforganic compounds described herein which satisfy the valencies of theheteroatoms. This disclosure is not intended to be limited in any mannerby the permissible substituents of organic compounds. Also, the terms“substitution” or “substituted with” include the implicit proviso thatsuch substitution is in accordance with permitted valence of thesubstituted atom and the substituent, and that the substitution resultsin a stable compound, e.g., a compound that does not spontaneouslyundergo transformation such as by rearrangement, cyclization,elimination, etc.

“A¹,” “A²,” “A³,” and “A⁴” are used herein as generic symbols torepresent various specific substituents. These symbols can be anysubstituent, not limited to those disclosed herein, and when they aredefined to be certain substituents in one instance, they can, in anotherinstance, be defined as some other substituents.

The term “aliphatic” as used herein refers to a non-aromatic hydrocarbongroup and includes branched and unbranched, alkyl, alkenyl, or alkynylgroups.

The term “alkyl” as used herein is a branched or unbranched saturatedhydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, pentyl, hexyl, heptyl,octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl,tetracosyl, and the like. The alkyl group can also be substituted orunsubstituted. The alkyl group can be substituted with one or moregroups including, but not limited to, alkyl, halogenated alkyl, alkoxy,alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid,ester, ether, halide, hydroxy, ketone, nitro, silyl, sulfo-oxo,sulfonyl, sulfone, sulfoxide, or thiol, as described below.

Throughout the specification “alkyl” is generally used to refer to bothunsubstituted alkyl groups and substituted alkyl groups; however,substituted alkyl groups are also specifically referred to herein byidentifying the specific substituent(s) on the alkyl group. For example,the term “halogenated alkyl” specifically refers to an alkyl group thatis substituted with one or more halide, e.g., fluorine, chlorine,bromine, or iodine. The term “alkoxyalkyl” specifically refers to analkyl group that is substituted with one or more alkoxy groups, asdescribed below. The term “alkylamino” specifically refers to an alkylgroup that is substituted with one or more amino groups, as describedbelow, and the like. When “alkyl” is used in one instance and a specificterm such as “alkylalcohol” is used in another, it is not meant to implythat the term “alkyl” does not also refer to specific terms such as“alkylalcohol” and the like.

This practice is also used for other groups described herein. That is,while a term such as “cycloalkyl” refers to both unsubstituted andsubstituted cycloalkyl moieties, the substituted moieties can, inaddition, be specifically identified herein; for example, a particularsubstituted cycloalkyl can be referred to as, e.g., an“alkylcycloalkyl.” Similarly, a substituted alkoxy can be specificallyreferred to as, e.g., a “halogenated alkoxy,” a particular substitutedalkenyl can be, e.g., an “alkenylalcohol,” and the like. Again, thepractice of using a general term, such as “cycloalkyl,” and a specificterm, such as “alkylcycloalkyl,” is not meant to imply that the generalterm does not also include the specific term.

The term “alkoxy” as used herein is an alkyl group bound through asingle, terminal ether linkage; that is, an “alkoxy” group can bedefined as —OA¹ where A¹ is alkyl as defined above.

The term “alkenyl” as used herein is a hydrocarbon group of from 2 to 24carbon atoms with a structural formula containing at least onecarbon-carbon double bond. Asymmetric structures such as (A¹A²)C═C(A³A⁴)are intended to include both the E and Z isomers. This can be presumedin structural formulae herein wherein an asymmetric alkene is present,or it can be explicitly indicated by the bond symbol C═C. The alkenylgroup can be substituted with one or more groups including, but notlimited to, alkyl, halogenated alkyl, alkoxy, alkenyl, alkynyl, aryl,heteroaryl, aldehyde, amino, carboxylic acid, ester, ether, halide,hydroxy, ketone, nitro, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide,or thiol, as described below.

The term “alkynyl” as used herein is a hydrocarbon group of 2 to 24carbon atoms with a structural formula containing at least onecarbon-carbon triple bond. The alkynyl group can be substituted with oneor more groups including, but not limited to, alkyl, halogenated alkyl,alkoxy, alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, carboxylicacid, ester, ether, halide, hydroxy, ketone, nitro, silyl, sulfo-oxo,sulfonyl, sulfone, sulfoxide, or thiol, as described below.

The term “aryl” as used herein is a group that contains any carbon-basedaromatic group including, but not limited to, benzene, naphthalene,phenyl, biphenyl, phenoxybenzene, and the like. The term “heteroaryl” isdefined as a group that contains an aromatic group that has at least oneheteroatom incorporated within the ring of the aromatic group. Examplesof heteroatoms include, but are not limited to, nitrogen, oxygen,sulfur, and phosphorus. The term “non-heteroaryl,” which is included inthe term “aryl,” defines a group that contains an aromatic group thatdoes not contain a heteroatom. The aryl and heteroaryl groups can besubstituted or unsubstituted. The aryl and heteroaryl groups can besubstituted with one or more groups including, but not limited to,alkyl, halogenated alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl,aldehyde, amino, carboxylic acid, ester, ether, halide, hydroxy, ketone,nitro, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol asdescribed herein. The term “biaryl” is a specific type of aryl group andis included in the definition of aryl. Biaryl refers to two aryl groupsthat are bound together via a fused ring structure, as in naphthalene,or are attached via one or more carbon-carbon bonds, as in biphenyl.

The term “cycloalkyl” as used herein is a non-aromatic carbon-based ringcomposed of at least three carbon atoms. Examples of cycloalkyl groupsinclude, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, etc. The term “heterocycloalkyl” is a cycloalkyl group asdefined above where at least one of the carbon atoms of the ring issubstituted with a heteroatom such as, but not limited to, nitrogen,oxygen, sulfur, or phosphorus. The cycloalkyl group and heterocycloalkylgroup can be substituted or unsubstituted. The cycloalkyl group andheterocycloalkyl group can be substituted with one or more groupsincluding, but not limited to, alkyl, alkoxy, alkenyl, alkynyl, aryl,heteroaryl, aldehyde, amino, carboxylic acid, ester, ether, halide,hydroxy, ketone, nitro, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide,or thiol as described herein.

The term “cycloalkenyl” as used herein is a non-aromatic carbon-basedring composed of at least three carbon atoms and containing at least onedouble bound, i.e., C═C. Examples of cycloalkenyl groups include, butare not limited to, cyclopropenyl, cyclobutenyl, cyclopentenyl,cyclopentadienyl, cyclohexenyl, cyclohexadienyl, and the like. The term“heterocycloalkenyl” is a type of cycloalkenyl group as defined above,and is included within the meaning of the term “cycloalkenyl,” where atleast one of the carbon atoms of the ring is substituted with aheteroatom such as, but not limited to, nitrogen, oxygen, sulfur, orphosphorus. The cycloalkenyl group and heterocycloalkenyl group can besubstituted or unsubstituted. The cycloalkenyl group andheterocycloalkenyl group can be substituted with one or more groupsincluding, but not limited to, alkyl, alkoxy, alkenyl, alkynyl, aryl,heteroaryl, aldehyde, amino, carboxylic acid, ester, ether, halide,hydroxy, ketone, nitro, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide,or thiol as described herein.

The term “cyclic group” is used herein to refer to either aryl groups,non-aryl groups (i.e., cycloalkyl, heterocycloalkyl, cycloalkenyl, andheterocycloalkenyl groups), or both. Cyclic groups have one or more ringsystems that can be substituted or unsubstituted. A cyclic group cancontain one or more aryl groups, one or more non-aryl groups, or one ormore aryl groups and one or more non-aryl groups.

The term “aldehyde” as used herein is represented by the formula —C(O)H.Throughout this specification “C(O)” or “CO” is a short hand notationfor C═O.

The term “amino” as used herein is represented by the formula —NA¹A²,where A¹ and A² can each be substitution group as described herein, suchas hydrogen, an alkyl, halogenated alkyl, alkenyl, alkynyl, aryl,heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl, orheterocycloalkenyl group described above.

The term “carboxylic acid” as used herein is represented by the formula—C(O)OH. A “carboxylate” or “carboxyl” group as used herein isrepresented by the formula —C(O)O⁻.

The term “ester” as used herein is represented by the formula —OC(O)A¹or —C(O)OA¹, where A¹ can be an alkyl, halogenated alkyl, alkenyl,alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl,or heterocycloalkenyl group described above.

The term “ether” as used herein is represented by the formula A¹OA²,where A¹ and A² can be, independently, an alkyl, halogenated alkyl,alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl,heterocycloalkyl, or heterocycloalkenyl group described above.

The term “ketone” as used herein is represented by the formula A¹C(O)A²,where A¹ and A² can be, independently, an alkyl, halogenated alkyl,alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl,heterocycloalkyl, or heterocycloalkenyl group described above.

The term “halide” or “halogen” as used herein refers to the fluorine,chlorine, bromine, and iodine.

The term “hydroxyl” as used herein is represented by the formula —OH.

The term “nitro” as used herein is represented by the formula —NO₂.

The term “silyl” as used herein is represented by the formula —SiA¹A²A³,where A¹, A², and A³ can be, independently, hydrogen, alkyl, halogenatedalkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl,cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group describedabove.

The term “sulfonyl” is used herein to refer to the sulfo-oxo grouprepresented by the formula —S(O)₂A¹, where A¹ can be hydrogen, an alkyl,halogenated alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl,cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl group describedabove.

The term “sulfonylamino” or “sulfonamide” as used herein is representedby the formula —S(O)₂NH—.

The term “thiol” as used herein is represented by the formula —SH.

The term “thio” as used herein is represented by the formula —S—.

“R¹,” “R²,” “R³,” “R^(n),” etc., where n is some integer, as used hereincan, independently, possess one or more of the groups listed above. Forexample, if R¹ is a straight chain alkyl group, one of the hydrogenatoms of the alkyl group can optionally be substituted with a hydroxylgroup, an alkoxy group, an amine group, an alkyl group, a halide, andthe like. Depending upon the groups that are selected, a first group canbe incorporated within second group or, alternatively, the first groupcan be pendant (i.e., attached) to the second group. For example, withthe phrase “an alkyl group comprising an amino group,” the amino groupcan be incorporated within the backbone of the alkyl group.Alternatively, the amino group can be attached to the backbone of thealkyl group. The nature of the group(s) that is (are) selected willdetermine if the first group is embedded or attached to the secondgroup.

It is to be understood that the compounds provided herein can containchiral centers. Such chiral centers can be of either the (R-) or (S-)configuration. The compounds provided herein can either beenantiomerically pure, or be diastereomeric or enantiomeric mixtures.

As used herein, substantially pure means sufficiently homogeneous toappear free of readily detectable impurities as determined by standardmethods of analysis, such as thin layer chromatography (TLC), nuclearmagnetic resonance (NMR), gel electrophoresis, high performance liquidchromatography (HPLC) and mass spectrometry (MS), gas-chromatographymass spectrometry (GC-MS), and similar, used by those of skill in theart to assess such purity, or sufficiently pure such that furtherpurification would not detectably alter the physical and chemicalproperties, such as enzymatic and biological activities, of thesubstance. Both traditional and modern methods for purification of thecompounds to produce substantially chemically pure compounds are knownto those of skill in the art. A substantially chemically pure compoundcan, however, be a mixture of stereoisomers.

Unless stated to the contrary, a formula with chemical bonds shown onlyas solid lines and not as wedges or dashed lines contemplates eachpossible isomer, e.g., each enantiomer, diastereomer, and meso compound,and a mixture of isomers, such as a racemic or scalemic mixture.

Reference will now be made in detail to specific aspects of thedisclosed materials, compounds, compositions, articles, and methods,examples of which are illustrated in the accompanying Examples.

C. Materials and Compositions

N-Functionalized Imidazoles

Systems comprising N-functionalized imidazoles are provided herein.These compounds are useful for reducing volatile compounds, such ascarbon dioxide (CO₂), carbon monoxide (CO), sulfur dioxide (SO₂),hydrogen sulfide (H₂S), nitrogen oxide (NO), nitrogen dioxide (NO₂),carbonyl sulfide (COS), and carbon disulfide (CS₂), mercaptans, H₂O, O₂,H₂, N₂, C₁-C₈ hydrocarbons (e.g., methane and propane), volatile organiccompounds, and mixtures of these and other volatile compounds from gasstreams and liquid streams. The N-functionalized imidazoles arenon-ionic compounds under neutral compounds (i.e., the imidazoles do notcontain a charge under neutral conditions). Neutral conditions includeconditions where no proton is available to react with theN-functionalized imidazole (i.e., to protonate the N-functionalizedimidazole). Protons can be present, but the conditions of the system,including the basicity of the N-functionized imidazole, are such that nosignificant amount of protonation of the N-functionalized imidazoleoccurs, i.e., the conditions do not produce imidazolium ion. Neutralconditions for the N-functionalized imidazoles include conditions wherethe pH of the system is from about 6.7 to about 7.3. In some examples,the pH of the system can be about 6.7, about 6.8, about 6.9, about 7.0,about 7.1, about 7.2, about 7.3, or the like, where any of the statedvalues can form an upper or lower endpoint of a range. The term “neutralconditions” is used herein relative to the specific imidazole, thus thisterm means conditions wherein the imidazole is not protonated (i.e.,made cationic). For example, the pH of the system can be from about 6.8to about 7.2, or from about 6.9 to about 7.1. Further, theN-functionalized imidazoles described herein are not components of anionic-liquid (i.e., liquids that contain ions under all conditions).

The N-functionalized imidazoles described herein are represented byFormula I:

and derivatives thereof.

In Formula I, R¹ is substituted or unsubstituted C₁₋₂₀ alkyl,substituted or unsubstituted C₂₋₂₀ alkenyl, substituted or unsubstitutedC₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀ heteroalkyl,substituted or unsubstituted C₂₋₂₀ heteroalkenyl, substituted orunsubstituted C₂₋₂₀ heteroalkynyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, substituted or unsubstituted heteroaryl,substituted or unsubstituted thio, substituted or unsubstituted amino,substituted or unsubstituted alkoxyl, substituted or unsubstitutedaryloxyl, silyl, siloxyl, or cyano.

Also in Formula I, R², R³, and R⁴ are each independently selected fromhydrogen, halogen, hydroxyl, substituted or unsubstituted C₁₋₂₀ alkyl,substituted or unsubstituted C₂₋₂₀ alkenyl, substituted or unsubstitutedC₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀ heteroalkyl,substituted or unsubstituted C₂₋₂₀ heteroalkenyl, substituted orunsubstituted C₂₋₂₀ heteroalkynyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, substituted or unsubstituted heteroaryl,substituted or unsubstituted thio, substituted or unsubstituted alkoxyl,substituted or unsubstituted aryloxyl, substituted or unsubstitutedamino, cyano, or nitro.

Further in Formula I, adjacent R groups, i.e., R¹ and R², R¹ and R⁴, andR² and R³, can be combined to form a substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted cycloalkenyl, substituted orunsubstituted cycloalkynyl, substituted or unsubstitutedheterocycloalkyl, substituted or unsubstituted heterocycloalkenyl, orsubstituted or unsubstituted heterocycloalkynyl. R², R³, R⁴, and R⁵ caneach also be halides, cyano, nitro, and other similar groups.

In some embodiments, the N-functionalized imidazoles represented byFormula I can be selected from an N-alkyl imidazole, an N-alkenylimidazole, an N-alkynyl imidazole, an N-aryl imidazole, or mixturesthereof. In some examples of Formula I, R¹ can be unsubstituted alkyl asrepresented by Formula I-A. In other examples of Formula I, R¹ can be aheteroalkyl group such as an ethoxylated group as represented by FormulaI-B. In still further examples of Formula I, R¹ can be a substitutedalkyl group, such as, for example, cyanoalkyl or hydroxyalkyl asrepresented by Formula I-C and Formula I-D, respectively.

In Formula I-A, m is an integer from 0 to 20. In Formulas I-B, I-C, andI-D, n, p, and q, respectively, are independently integers from 1 to 20.In some embodiments, R², R³, and R⁴ are each hydrogen.

In some examples of Formula I, R¹ can be an alkyl, alkenyl, alkynyl,heteroalkyl, heteroalkenyl, heteroalkynyl, cycloalkyl, heterocycloalkyl,aryl, heteroaryl, thio, amino, alkoxyl, aryloxyl, or silyl substitutedwith an imidazole group to form a bis-N-substituted imidazole. Forexample, Formula I can be represented by Formula I-E as shown below.

In Formula I-E, L is selected from substituted or unsubstituted C₁₋₂₀alkyl, substituted or unsubstituted C₂₋₂₀ alkenyl, substituted orunsubstituted C₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀heteroalkyl, substituted or unsubstituted C₂₋₂₀ heteroalkenyl,substituted or unsubstituted C₂₋₂₀ heteroalkynyl, substituted orunsubstituted cycloalkyl, substituted or unsubstituted heterocycloalkyl,substituted or unsubstituted aryl, substituted or unsubstitutedheteroaryl, substituted or unsubstituted thio, substituted orunsubstituted amino, substituted or unsubstituted alkoxyl, substitutedor unsubstituted aryloxyl, or silyl.

Also in Formula I-E, R⁵, R⁶, and R⁷ are each independently selected fromhydrogen, halogen, hydroxyl, substituted or unsubstituted C₁₋₂₀ alkyl,substituted or unsubstituted C₂₋₂₀ alkenyl, substituted or unsubstitutedC₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀ heteroalkyl,substituted or unsubstituted C₂₋₂₀ heteroalkenyl, substituted orunsubstituted C₂₋₂₀ heteroalkynyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, substituted or unsubstituted heteroaryl,substituted or unsubstituted thio, substituted or unsubstituted alkoxyl,substituted or unsubstituted aryloxyl, substituted or unsubstitutedamino, or cyano.

In some examples of Formula I-E, the imidazole is an imidazole dimer. Inother words, in some examples of Formula I-E, R² and R⁵ are the samesubstituent, R³ and R⁶ are the same substituent, and R⁴ and R⁷ are thesame substituent.

Particular examples of Formula I include the following compounds:

Amines

In some embodiments, the N-functionalized imidazole containing systemscan further comprise one or more amine compounds. The amine can be aprimary amine, a secondary amine, a tertiary amine, a cyclic amine, or amixture thereof. The amine compounds described herein can be representedby Formula II:

In Formula II, R¹, R², and R³ can each independently be selected fromthe group consisting of hydrogen, substituted or unsubstituted C₁₋₂₀alkyl, substituted or unsubstituted C₂₋₂₀ alkenyl, substituted orunsubstituted C₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀heteroalkyl, substituted or unsubstituted C₂₋₂₀ heteroalkenyl,substituted or unsubstituted C₂₋₂₀ heteroalkynyl, substituted orunsubstituted cycloalkyl, substituted or unsubstituted heterocycloalkyl,substituted or unsubstituted aryl, substituted or unsubstitutedheteroaryl, substituted or unsubstituted thio, substituted orunsubstituted amino, substituted or unsubstituted alkoxyl, substitutedor unsubstituted aryloxyl, silyl, siloxyl, or cyano.

In some embodiments, the amine can be a primary amine. According tothese examples, two of R², or R³ are hydrogen and the remaining group isother than hydrogen to form a compound according to Formula II-A.

In Formula II-A, R¹ is selected from substituted or unsubstituted C₁₋₂₀alkyl, substituted or unsubstituted C₂₋₂₀ alkenyl, substituted orunsubstituted C₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀heteroalkyl, substituted or unsubstituted C₂₋₂₀ heteroalkenyl,substituted or unsubstituted C₂₋₂₀ heteroalkynyl, substituted orunsubstituted cycloalkyl, substituted or unsubstituted heterocycloalkyl,substituted or unsubstituted aryl, substituted or unsubstitutedheteroaryl, substituted or unsubstituted thio, substituted orunsubstituted amino, substituted or unsubstituted alkoxyl, orsubstituted or unsubstituted aryloxyl. Particular examples of primaryamines as described herein include monoethanolamine (MEA), diglycolamine(DGA), 2-amino-2-methylpropanol (AMP), and 1-(3-aminopropyl)-imidazole(API).

In some embodiments, the amine can be a secondary amine where one of R¹,R², or R³ is hydrogen and the remaining two groups are other thanhydrogen. Secondary amines as described herein can be represented byFormula II-B.

In Formula II-B, R¹ and R² are each independently selected fromsubstituted or unsubstituted C₁₋₂₀ alkyl, substituted or unsubstitutedC₂₋₂₀ alkenyl, substituted or unsubstituted C₂₋₂₀ alkynyl, substitutedor unsubstituted C₁₋₂₀ heteroalkyl, substituted or unsubstituted C₂₋₂₀heteroalkenyl, substituted or unsubstituted C₂₋₂₀ heteroalkynyl,substituted or unsubstituted cycloalkyl, substituted or unsubstitutedheterocycloalkyl, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted thio, substitutedor unsubstituted amino, substituted or unsubstituted alkoxyl, orsubstituted or unsubstituted aryloxyl. Particular examples of secondaryamines as described herein include N-methylethanolamine (NMEA),diethanolamine (DEA), and diisopropanolamine (DIPA).

In further embodiments, the amine can be a tertiary amine where each ofR¹, R², and R³ are other than hydrogen as represented by Formula II-C.

In Formula II-C, R¹, R², and R³ are each independently selected fromsubstituted or unsubstituted C₁₋₂₀ alkyl, substituted or unsubstitutedC₂₋₂₀ alkenyl, substituted or unsubstituted C₂₋₂₀ alkynyl, substitutedor unsubstituted C₁₋₂₀ heteroalkyl, substituted or unsubstituted C₂₋₂₀heteroalkenyl, substituted or unsubstituted C₂₋₂₀ heteroalkynyl,substituted or unsubstituted cycloalkyl, substituted or unsubstitutedheterocycloalkyl, substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted thio, substitutedor unsubstituted amino, substituted or unsubstituted alkoxyl, orsubstituted or unsubstituted aryloxyl. A particular example of atertiary amine includes N-methyldiethanolamine (MDEA).

The amines for use in the systems described herein can also includecyclic amines. According to these examples, two of R¹, R², or R³ cancombine to form a substituted or unsubstituted aryl, substituted orunsubstituted heteroaryl, substituted or unsubstituted cycloalkyl,substituted or unsubstituted cycloalkenyl, substituted or unsubstitutedcycloalkynyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted heterocycloalkenyl, or substituted or unsubstitutedheterocycloalkynyl. The cyclic amines can be represented by FormulaII-D.

In Formula II-D, the line connecting R¹ and R² represents a connection(e.g., a single bond or double bond) between R¹ and R² that forms acyclic structure including R¹, N, and R². Examples of suitable cyclicamines for use in the systems described herein include a substituted orunsubstituted piperazine (PZ) and an unsubstituted imidazole.

The amine described herein can contain one amino functional group (i.e.,can be a monoamine) or can contain two amino functional groups (L e.,can be a diamine), or can contain more than two amino functional groups(i.e., can be a polyamine).

Systems

The systems disclosed herein can contain one or more N-functionalizedimidazoles and optionally, one or more amines. The systems describedherein are not ionic liquids. For example, the combination of one ormore N-functionalized imidazoles and one or more amines does not resultin a low melting salt. Upon addition of an acid gas (e.g., CO₂, H₂S,etc.) the system can contain charge. Further, the systems describedherein can be distilled whereas ionic liquids do not have thiscapability. The systems disclosed herein can be neat (i.e., can becomposed of the N-functionalized imidazole and/or amine without anyadditional solvent) or can be dissolved or dispersed in one or moreadditional solvents. In some embodiments, the system is a neat systemcomprised primarily of one or more N-functionalized imidazoles. Systemscomprised primarily of the N-functionalized imidazole can contain about3% or less of impurities (i.e., the system contains about 97% or higher,about 98% or higher, or about 99% or higher N-functionalized imidazolebased on the weight of the system).

In some embodiments, the system is a neat system composed of a mixtureof one or more N-functionalized imidazoles as described herein and oneor more amines as described herein (i.e., an imidazole-amine blend). Theaddition to one or more amines to one or more N-functionalizedimidazoles results in a system with low volatility, low viscosity, andhigh CO₂ capacity. The properties of the system can be altered bychanging the ratios of N-functionalized imidazole and amine present inthe system.

The N-functionalized imidazole can comprise 99%, 98%, 97%, 96%, 95%,94%, 93%, 92%, 91%, 90%, 89%, 88%, 87%, 86%, 85%, 84%, 83%, 82%, 81%,80%, 79%, 78%, 77%, 76%, 75%, 74%, 73%, 72%, 71%, 70%, 69%, 68%, 67%,66%, 65%, 64%, 63%, 62%, 61%, 60%, 59%, 58%, 57%, 56%, 55%, 54%, 53%,52%, 51%, 50%, 49%, 48%, 47%, 46%, 45%, 44%, 43%, 42%, 41%, 40%, 39%,38%, 37%, 36%, 35%, 34%, 33%, 32%, 31%, 30%, 29%, 28%, 27%, 26%, 25%,24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%,10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of the system, where any ofthe stated values can form an upper or lower endpoint of a range. Infurther examples, the N-functionalized imidazole can comprise from 1% to99%, 10% to 90%, 20% to 80%, 30% to 70%, 40% to 60%, or 50% of thesystem. For example, the N-functionalized imidazole can comprise 67% ofthe system.

Likewise, the amine can comprise 99%, 98%, 97%, 96%, 95%, 94%, 93%, 92%,91%, 90%, 89%, 88%, 87%, 86%, 85%, 84%, 83%, 82%, 81%, 80%, 79%, 78%,77%, 76%, 75%, 74%, 73%, 72%, 71%, 70%, 69%, 68%, 67%, 66%, 65%, 64%,63%, 62%, 61%, 60%, 59%, 58%, 57%, 56%, 55%, 54%, 53%, 52%, 51%, 50%,49%, 48%, 47%, 46%, 45%, 44%, 43%, 42%, 41%, 40%, 39%, 38%, 37%, 36%,35%, 34%, 33%, 32%, 31%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%,21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%,6%, 5%, 4%, 3%, 2%, or 1% of the system, where any of the stated valuescan form an upper or lower endpoint of a range. In further examples, theamine can comprise from 1% to 99%, 10% to 90%, 20% to 80%, 30% to 70%,40% to 60%, or 50% of the system. For example, the amine can comprise33% of the system.

In some embodiments, the system can have an N-functionalized imidazoleto amine ratio of 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, and thelike. In other embodiments, the system can have an amine toN-functionalized imidazole ratio of 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1,2:1, 1:1, and the like.

As described above, the systems described herein can be dissolved ordispersed in one or more additional solvents. For example, the one ormore N-functionalized imidazole or the one or more N-functionalizedimidazole and one or more amine blend can be mixed with a solvent suchas water, tetrahydrofuran (THF), dichloromethane, acetonitrile, toluene,dimethyl sulfoxide (DMSO), pyridine, dimethylformamide, dioxane, glycolsolvents, methanol, ethanol, propanol, butanol, ethyl acetate, methylethyl ketone, acetone, and the like to provide a system. In theseexamples, the N-functionalized imidazole or the N-functionalizedimidazole and amine blend can comprise from about 0.1% to about 99.9% ofthe system. For example, the N-functionalized imidazoles or theN-functionalized imidazole and amine blend can comprise from about 99%,98%, 97%, 96%, 95%, 94%, 93%, 92%, 91%, 90%, 89%, 88%, 87%, 86%, 85%,84%, 83%, 82%, 81%, 80%, 79%, 78%, 77%, 76%, 75%, 74%, 73%, 72%, 71%,70%, 69%, 68%, 67%, 66%, 65%, 64%, 63%, 62%, 61%, 60%, 59%, 58%, 57%,56%, 55%, 54%, 53%, 52%, 51%, 50%, 49%, 48%, 47%, 46%, 45%, 44%, 43%,42%, 41%, 40%, 39%, 38%, 37%, 36%, 35%, 34%, 33%, 32%, 31%, 30%, 29%,28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%,14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of thesystem, where any of the stated values can form an upper or lowerendpoint of a range. In further examples, the N-functionalized imidazoleor the N-functionalized imidazole and amine blend can comprise from 1%to 99%, 10% to 90%, 20% to 80%, 30% to 70%, 40% to 60%, or 50% of thesystem.

The systems described herein are substantially free from volatileorganic compounds. By substantially free is meant that volatile organiccompounds are present at less than about 3%, 2%, 1%, 0.9%, 0.8%, 0.7%,0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.001%, 0.0001%, or the like ofvolatile organic compounds. Further, these systems are characterized bylow viscosity in comparison with imidazolium-based ionic liquids. Forexample, the systems described herein are at least 10 times, 9 times, 8times, 7 times, 6 times, 5 times, 4 times, 3 times, or 2 times lessviscous than imidazolium-based ionic liquids. The intrinsic viscosity ofthe systems described herein can be measured, for example, according tothe method described in ASTM D5225-09 using a differential viscometer.For example, the intrinsic viscosity of the systems can be measuredusing a Brookfield DV-II+ Pro Viscometer equipped with a ULA (lowviscosity) spindle (Brookfield Engineering Laboratories, Inc.;Middleboro, Mass.). Further, the intrinsic viscosities of the systemscan be measured neat (i.e., with no additional solvent added). In someembodiments, the viscosities of the systems at 24° C. can be less than20 cP, less than 19 cP, less than 18 cP, less than 17 cP, less than 16cP, less than 15 cP, less than 14 cP, less than 13 cP, less than 12 cP,less than 11 cP, less than 10 cP, less than 9 cP, less than 8 cP, lessthan 7 cP, less than 6 cP, less than 5 cP, less than 4 cP, less than 3cP, less than 2 cP, less than 1 cP, less than 0.9 cP, less than 0.8 cP,less than 0.7 cP, less than 0.6 cP, less than 0.5 cP, less than 0.4 cP,less than 0.3 cP, less than 0.2 cP, less than 0.1 cP, or the like, whereany of the stated values can form an upper or lower endpoint of a range.In further embodiments, the N-functionalized imidazoles can have aviscosity from about 0.1 cP to about 20 cP, about 0.2 cP to about 19 cP,about 0.3 cP to about 18 cP, about 0.4 cP to about 17 cP, about 0.5 cPto about 16 cP, about 0.6 cP to about 15 cP, about 0.7 cP to about 14cP, about 0.8 cP to about 13 cP, about 0.9 cP to about 12 cP, about 1 cPto about 11 cP, about 2 cP to about 10 cP, about 3 cP to about 9 cP,about 4 cP to about 8 cP, or about 5 cP to about 7 cP. For example, at24° C., a system comprised of 1-ethylimidazole has a viscosity of about2.02 cP. In another example, a system comprised of 1-butylimidazole hasa viscosity of about 3.38 cP at 24° C. In a further example, a systemcomprised of 1-hexylimidazole has a viscosity of about 2.99 cP at 45° C.Still further, a system comprised of 1-octylimidazole has a viscosity ofabout 7.77 cP at 25° C.

The N-functionalized imidazoles according to Formula I and the aminesaccording to Formula II can be prepared in a variety of ways known toone skilled in the art of organic synthesis or variations thereon asappreciated by those skilled in the art. The compounds described hereincan be prepared from readily available starting materials. Optimumreaction conditions can vary with the particular reactants or solventsused, but such conditions can be determined by one skilled in the art.The use of protection and deprotection, and the selection of appropriateprotecting groups can be determined by one skilled in the art. Thechemistry of protecting groups can be found, for example, in Wuts andGreene, Protective Groups in Organic Synthesis, 4th Ed., Wiley & Sons,2006, which is incorporated herein by reference in its entirety.

Variations on Formula I and Formula II include the addition,subtraction, or movement of the various constituents as described foreach compound. Similarly, when one or more chiral centers are present ina molecule, the chirality of the molecule can be changed. Additionally,compound synthesis can involve the protection and deprotection ofvarious chemical groups.

The N-functionalized imidazoles and amines or the starting materials andreagents used in preparing the disclosed compounds are either availablefrom commercial suppliers such as Aldrich Chemical Co., (Milwaukee,Wis.), Acros Organics (Morris Plains, N.J.), Fisher Scientific(Pittsburgh, Pa.), Sigma (St. Louis, Mo.), Pfizer (New York, N.Y.),GlaxoSmithKline (Raleigh, N.C.), Merck (Whitehouse Station, N.J.),Johnson & Johnson (New Brunswick, N.J.), Aventis (Bridgewater, N.J.),AstraZeneca (Wilmington, Del.), Novartis (Basel, Switzerland), Wyeth(Madison, N.J.), Bristol-Myers-Squibb (New York, N.Y.), Roche (Basel,Switzerland), Lilly (Indianapolis, Ind.), Abbott (Abbott Park, Ill.),Schering Plough (Kenilworth, N.J.), or Boehringer Ingelheim (Ingelheim,Germany), or are prepared by methods known to those skilled in the artfollowing procedures set forth in references such as Fieser and Fieser'sReagents for Organic Synthesis, Volumes 1-17 (John Wiley and Sons,1991); Rodd's Chemistry of Carbon Compounds, Volumes 1-5 andSupplementals (Elsevier Science Publishers, 1989); Organic Reactions,Volumes 1-40 (John Wiley and Sons, 1991); March's Advanced OrganicChemistry, (John Wiley and Sons, 4th Edition); and Larock'sComprehensive Organic Transformations (VCH Publishers Inc., 1989).

Reactions to produce the compounds described herein can be carried outin solvents, which can be selected by one of skill in the art of organicsynthesis. Solvents can be substantially nonreactive with the startingmaterials (reactants), the intermediates, or products under theconditions at which the reactions are carried out, i.e., temperature andpressure. Reactions can be carried out in one solvent or a mixture ofmore than one solvent. Product or intermediate formation can bemonitored according to any suitable method known in the art. Forexample, product formation can be monitored by spectroscopic means, suchas nuclear magnetic resonance spectroscopy (e.g., ¹H or ¹³C) infraredspectroscopy, spectrophotometry (e.g., UV-visible), or massspectrometry, or by chromatography such as high perfonnance liquidchromatography (HPLC) or thin layer chromatography.

As shown in Scheme 1, the N-substituted imidazoles described by FormulaI can be made, for example, by treating commercially available imidazole(1) with a strong base (e.g., sodium hydride or sodium hydroxide) toform the imidazolate sodium salt (2). The imidazolate sodium salt (2)can then be treated with an alkyl halide to form the N-alkylatedimidazole (3). Similarly, other organohalides can be used in place ofthe alkyl halide to provide the corresponding N-organosubstitutedimidazoles.

In addition, the bis-N-substituted imidazoles described by Formula I-Ecan be made, for example, by treating two equivalents of imidazoliumsodium salt (2) with an alkyl dihalide to form compound (4) (see Scheme2).

Further, the N-substituted imidazoles according to Formula I can besynthesized according to methods described in U.S. Published PatentApplication Number 2009/0171098, which is incorporated by referenceherein for its teaching of methods of synthesis of N-substitutedimidazoles.

The disclosed imidazole-amine blends can be prepared by methodsdescribed herein. Generally, the particular N-functionalizedimidazole(s) and amine(s) used to prepare the systems are selected asdescribed herein. Then, with the particular N-functionalizedimidazole(s) and amine(s) in hand, they can be combined, resulting in asystem as described herein.

Providing N-functionalized imidazoles and amines used to prepare thesystems depends, in one aspect, on the desired properties of theresulting system. As described herein, the disclosed compositions canhave multiple desired properties (e.g., low viscosity, low volatility,high CO₂ capacity, etc.), which, at least in part, come from theproperties of the imidazoles and amines used to prepare the systems.Thus, to prepare the disclosed systems, one or more N-functionalizedimidazoles with desired properties and one or more amines with desiredproperties are selected and provided. Providing a desired imidazole andamine can be done in any order, depending on the preference and aims ofthe practitioner. For example, a particular imidazole can be providedand then a particular amine can be provided. Alternatively, a particularamine can be provided and then a particular imidazole can be provided.Further, the imidazole and amine can be provided simultaneously.Properties desired to be adjusted based on the selection of theimidazole and the amine can include, for example, the vapor pressure,viscosity, density, heat capacity, thermal conductivity, and surfacetension. For example, in high pressure applications, the systems can becomprised primarily of N-functionalized imidazoles. In low pressureapplications, the systems can comprise a combination of theN-functionalized imidazoles and one or more amines. Further, the aminesused in the systems can be varied based on the pressure level of theapplication. Primary (1°) amines, such as monoethanolamine (MEA) ordiglycolamine (DGA), can be suitable for use in low pressureapplications. An example of a low pressure application includespost-combustion CO₂ capture from power plants. Secondary (2°) amines,such as N-methylethanolamine (NMEA) or piperazine (PZ), or stericallyhindered 2° amines, such as diisopropranolamine (DIPA), can be suitablefor use in moderate to high pressure applications. An example of amoderate to high pressure application is the removal of CO₂ from naturalgas.

D. Methods of Using the Systems

The systems described herein can be used to reduce volatile compoundsfrom streams (e.g., gas streams or liquid streams) as described in U.S.Published Patent Application Number 2009/0291874, which is incorporatedby reference herein for its methods and techniques of volatile compoundreduction. As used herein, volatile compounds can include to undesirablegaseous components found in a source and having a molecular weight lowerthan 150 g/mol. For example, the volatile compounds can have a molecularweight lower than 140 g/mol, 130 g/mol, 120 g/mol, 110 g/mol, 100 g/mol,90 g/mol, 80 g/mol, 70 g/mol, 60 g/mol, 50 g/mol, 40 g/mol, 30 g/mol, 20g/mol, or the like, where any of the stated values can form an upper orlower endpoint of a range. Examples of volatile compounds include CO₂,CO, COS, H₂S, SO₂, NO, N₂O, mercaptans, H₂O, O₂, H₂, N₂, C₁-C₈hydrocarbons (e.g., methane and propane), volatile organic compounds,and mixtures of these.

The method for reducing a volatile compound from a stream can includecontacting the stream with an effective amount of a system as describedherein. In some embodiments, the system is comprised primarily of anN-functionalized imidazole. In other embodiments, the system contains anN-functionalized imidazole and an amine. For example, volatile compoundsfrom a gas stream (e.g., a natural gas stream or a flue gas stream) canbe reduced according to this method.

Further described herein is a method for sweetening a natural gas feedstream. The method includes contacting the natural gas feed stream withan effective amount of a system as described herein to form a purifiednatural gas feed stream and a gas-rich system. Optionally, the naturalgas feed stream can be contacted with a second system as describedherein. The contacting of the natural gas feed stream with the secondsystem can be performed simultaneously as the contacting with the firstsystem (i.e., the gas feed stream can be contacted with both the firstand second system) or can be performed sequentially (i.e., the gas feedstream can be contacted with the second system after the gas feed streamhas been contacted with the first system). The purified natural gas feedstream can then be separated from the gas-rich system. In someembodiments, the volatile compounds are reduced from the gas-rich systemto regenerate the system. The system can be regenerated by heating orpressurizing the gas-rich system.

The examples below are intended to further illustrate certain aspects ofthe methods and compositions described herein, and are not intended tolimit the scope of the claims.

EXAMPLES

The following examples are set forth below to illustrate the methods andresults according to the disclosed subject matter. These examples arenot intended to be inclusive of all aspects of the subject matterdisclosed herein, but rather to illustrate representative methods andresults. These examples are not intended to exclude equivalents andvariations of the present invention which are apparent to one skilled inthe art.

Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, etc.) but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are parts by weight,temperature is in ° C. or is at ambient temperature, and pressure is ator near atmospheric. There are numerous variations and combinations ofreaction conditions, e.g., component concentrations, temperatures,pressures and other reaction ranges and conditions that can be used tooptimize the product purity and yield obtained from the describedprocess. Only reasonable and routine experimentation will be required tooptimize such process conditions.

Example 1 Materials

1-methylimidazole (1) was obtained from Sigma-Aldrich (Milwaukee, Wis.USA) and used without further purification. 1-n-alkylimidazoles (2-10)were synthesized from sodium imidazolate (NaIm) and a correspondingalkyl bromide as described in Bara et al., “Versatile and ScalableMethod for Producing N-Functionalized Imidazoles,” Ind. Eng. Chem. Res.,50(24); 13614-13619 (2011) and in U.S. Published Patent ApplicationNumber 2009/0171098, which are incorporated by reference herein in theirentireties for their teaching of N-functionalized imidazoles andsynthesis thereof. Research Grade CO₂ and CH₄ were purchased from AirGas(Radnor, Pa. USA).

Example 2 Density Measurements

Density values for each 1-n-alkylimidazole were obtained using a MettlerToledo DM45 DeltaRange density meter, which operates viaelectromagnetically induced oscillation of a glass U-form tube, withautomatic compensation for variations in atmospheric pressure. Thedensity meter can measure liquid samples within the range of 0-3 g/cm³with a minimal sample size of 1.2 cm³. The accuracy of the density metermeasurements is ±0.00005 g/cm³ for all operating temperatures. Densitiesof 1-n-alkylimidazoles were recorded over a temperature range of 20-80°C. at 10° C. increments, for a total of seven density measurements percompound. The unit was washed between every run with deionized H₂O,followed by an acetone rinse, and then dried by air flow. The densityreading of the clean, empty cell was verified to be consistent with thatof air at 20° C. (0.00120 g/cm³) before continuing to the next sample.

The measured density values for 1-n-alkylimidazoles over the temperaturerange of 20-80° C. are presented in Table 1.

TABLE 1 Density (g/cm³) Temperature (° C.) 1-n-alkylimidazole 20 30 4050 60 70 80  1 - Methyl 1.03525 1.02644 1.01760 1.00871 0.99979 0.990830.98178  2 - Ethyl 0.99448 0.98581 0.97712 0.96843 0.95969 0.950890.94208  3 - Propyl 0.97290 0.96456 0.95624 0.94789 0.93952 0.931110.92267  4 - Butyl 0.95137 0.94338 0.93540 0.92740 0.91938 0.911320.90320  5 - Pentyl 0.93887 0.93111 0.92334 0.91556 0.90776 0.899940.89208  6 - Hexyl 0.92990 0.92226 0.91463 0.90698 0.89932 0.891660.88395  7 - Octyl 0.91154 0.90429 0.89706 0.88983 0.88259 0.875310.86801  8 - Decyl 0.90145 0.89437 0.88729 0.88022 0.87315 0.866080.85900  9 - Dodecyl 0.89474 0.88776 0.88083 0.87390 0.86699 0.860080.85315 10 - Tetradecyl 0.88940 0.88255 0.87574 0.86895 0.86218 0.855410.84862

With the exception of 1-methylimidazole in the range of 20-50° C., allof the measured densities for 1-n-alkylimidazoles were less than 1.00000g/cm³. For each compound, density was observed to decrease linearly withincreasing temperature, and across the entire group of1-n-alkylimidazoles, density decreased with increasing length of then-alkyl substituent.

Example 3 Viscosity Measurements

Viscosity data were obtained using a Brookfield DV-II+ Pro viscometer.The viscosity measurement is based on a torque value and shear rate of acertain sized spindle in contact with a pre-determined amount of fluid.The “ULA” spindle and jacketed sample cell was used for these relativelylow viscosity liquids (<25 cP), which required a minimal sample size ofapproximately 16 cm³. The viscometer accuracy is ±1% of the reading fortorque measurement with a repeatability of ±0.2% of the reading. Theviscosity of each 1-n-alkylimidazole was measured at ten temperatureswithin the range of 20-80° C. The temperature of the jacketed samplechamber was controlled via the Brookfield TC-602P circulating bath,which has an operating range of −20-200° C. and a temperature stabilityof ±0.01° C. The sample cell was cleaned between every run by rinsingwith deionized water and acetone, followed by air drying. The viscometerwas re-zeroed between runs.

The measured viscosity values for 1-n-alkylimidazoles over thetemperature range of 20-80° C. are presented in Table 2.

TABLE 2 Viscosity (cP) Temperature (° C.) 1-n-alkylimidazole 20 25 30 3540 45 50 60 70 80  1 - Methyl 1.92 1.77 1.64 1.51 1.40 1.30 1.28 1.241.21 1.17  2 - Ethyl 2.22 2.04 1.86 1.70 1.56 1.45 1.34 1.30 1.23 1.22 3 - Propyl 3.17 2.81 2.50 2.26 2.05 1.86 1.69 1.45 1.25 1.23  4 - Butyl3.95 3.47 3.05 2.71 2.43 2.19 1.99 1.66 1.43 1.42  5 - Pentyl 5.13 4.493.89 3.42 3.02 2.70 2.42 2.00 1.68 1.43  6 - Hexyl 5.88 5.07 4.38 3.823.37 2.99 2.67 2.18 1.82 1.55  7 - Octyl 9.17 7.77 6.56 5.63 4.87 4.253.76 3.00 2.44 2.04  8 - Decyl 12.95 10.75 9.00 7.62 6.50 5.62 4.93 3.863.10 2.56  9 - Dodecyl 18.14 14.97 12.36 10.34 8.77 7.52 6.50 5.00 3.953.21 10 - Tetradecyl 24.69 20.31 16.60 13.72 11.47 9.73 8.35 6.30 4.923.94

As can be seen in Table 2, almost all of the measured viscosities forthe ten 1-n-alkylimidazole compounds were <10 cP, and only1-tetradecylimidazole exhibited a viscosity >20 cP below 30° C. For eachcompound, viscosity was observed to decrease in a non-linear fashionwith increasing temperature. Viscosity was strongly correlated to lengthof the n-alkyl substituent, with an order of magnitude differencebetween the least viscous and most viscous compounds at 20° C., thoughreducing to about 3.5× difference at the highest temperature.

Example 4 CO₂ Solubility Measurements

The solubility of CO₂ in each of the 1-n-alkylimidazoles was measuredusing a custom built apparatus (FIG. 1) based on an approach developedfor the natural gas industry (see Bara et al., Acc. Chem. Res. 2010, 43,152-159).

The cell body was constructed from a 2.5″ OD (6.35 cm OD) sanitaryfitting butt-welded to a corresponding bottom cap. ¼″ (0.635 cm) VCR and⅛″ (0.3175 cm) tube fittings were welded to the top cap, and a PTFEgasket and spring-loaded clamp were used to seal the vessel. Thesanitary fittings, gaskets, and clamps were purchased fromMcMaster-Carr. Swagelok fittings were purchased from Alabama FluidSystems Technologies (Pelham, Ala.). Machine work was performed byEngineering Technical Services at the University of Alabama. Welding wasperformed by McAbee Construction (Tuscaloosa, Ala.).

Experiments were conducted at ambient temperature (25±0.5° C.) and thetemperature controlled via air circulation. Approximately 40 mL of a1-n-alkylimidazole compound of interest was added to the cell and theweight of solvent recorded using a Mettler Toledo XS6002S PrecisionBalance, with a repeatability of 8 mg. The volume of solvent wascalculated using the density values measured as described above. A 1.75inch (4.445 cm) wide stir bar was added to ensure thorough contactbetween the gas and liquid phases. The vessel was then sealed and theresidual air removed via vacuum until the system pressure was less thanabout 5 torr as measured by an MKS Baratron pressure transducer(accuracy of ±0.5% of the reading) and displayed on a MKS PDR2000ATwo-Channel Digital Power Supply/Readout. The transducer was alsointerfaced with LabView (National Instruments) for digital dataacquisition and visual monitoring of system temperature and pressure.The sealed apparatus was then weighed to provide a tare weight prior toadding CO₂, the instrumentation re-connected and then unit secured abovea stir plate. CO₂ was added to the cell at pressures between 3-7 atm,and the equilibrium pressure and weight of added CO₂ were recorded.Confinnation that equilibrium had been reached was determined via astable pressure reading (±2 torr) over 10 minutes on both the readoutand from the data acquisition software. Because the solvent viscositywas low, and the vessel could be stirred, equilibrium was typicallyachieved in <30 min.

A CO₂ pressure of 3 atm was chosen as a starting point so as to ensure asufficient mass of CO₂ had been added to be far outside the error of thebalance. About 350-400 mg of CO₂ per atmosphere of CO₂ pressure wereabsorbed in 40 mL of solvent. The moles of CO₂ (n_(CO2)) added to thevessel were calculated from the mass increase and the molecular weightof CO₂ (44.01 g/mol). The moles of CO₂ in the vapor phase (n_(CO2)^(ν))(n_(CO2) ^(ν)) were calculated by subtracting the volume of thestir bar and solvent from that of the empty cell, and applying the idealgas law (Eqn. 1).P _(vapor)(V _(cell) −V _(stirbar) −V _(solvent))=n _(CO2) ^(ν) RT_(vapor) (1)

The moles of CO₂ in the liquid phase (n_(CO2) ¹)(n_(CO2) ^(ν)) weretaken to be the moles in the vapor phase subtracted from the total molesof CO₂ added to the cell (Eqn. 2).n _(CO) ₂ ¹ =n _(CO) ₂ −n _(CO) ₂ ^(ν)  (2)

The error in repeatability using this apparatus and technique was foundto be ±4%, which is in line with the error of similar equipmentpreviously described for making similar gas solubility measurements onILs. See, for example, Bara et aL, Acc. Chem. Res. 2010, 43, 152-159;Armand et al., Nat. Mater. 2009, 8, 621-629; and McCabe et al., UnitOperations of Chemical Engineering, 6th Ed.; McGraw-Hill: Boston, 2001.

It was assumed that the solvent density was constant upon addition ofCO₂ (i.e., no expansion). The solubility of CO₂ in each1-n-alkylimidazole was found to be linear in the pressure rangeexamined, and Henry's Law constants (H(atm)) were calculated from thefollowing relationship (Eqn. 3):

$\begin{matrix}{{H({atm})} = \frac{{P({atm})} \cdot \left( {n_{{CO}\; 2}^{1} + n_{imid}} \right)}{n_{{CO}\; 2}^{1}}} & (3)\end{matrix}$

Volumetric solubility (S) was calculated as standard cubic centimeters(cm³(STP)) of CO₂ dissolved per cm³ of 1-n-alkylimidazole (cm³ imid) peratmosphere of pressure, according to Eqn. 4:

$\begin{matrix}{S = \frac{{n_{{CO}\; 2}^{1} \cdot 22414}\mspace{14mu}\frac{{cm}^{3}({STP})}{{mol}\mspace{14mu}{CO}_{2}}}{{cm}_{imid}^{3}{P({atm})}}} & (4)\end{matrix}$

Solubility data for CO₂ in 1-n-alkylimidazoles at low pressures and25±0.5° C. in tewis of Henry's constants (H(atm)) and volumetricsolubility (S) are presented in Table 3.

TABLE 3 1-n-alkylimidazole H_(CO2) (atm) S (cm³ (STP) cm⁻³ atm⁻¹)  1 -Methyl 109 ± 2  2.71 ± 0.04  2 - Ethyl 97.9 ± 0.6 2.49 ± 0.07  3 -Propyl 88.9 ± 0.3 2.40 ± 0.06  4 - Butyl 77.4 ± 2.0 2.31 ± 0.04  5 -Pentyl 70.0 ± 1.3 2.25 ± 0.03  6 - Hexyl 67.8 ± 0.8 2.18 ± 0.09  7 -Octyl 58.3 ± 0.9 2.11 ± 0.04  8 - Decyl 53.6 ± 0.7 1.99 ± 0.06  9 -Dodecyl 51.7 ± 1.1 1.82 ± 0.06 10 - Tetradecyl 48.6 ± 1.7 1.77 ± 0.04Uncertainties represent ±1 standard deviation from the mean.

Example 5 Comparison of Density & Viscosity

For 1-n-alkylimidazoles, density is influenced by the length of then-alkyl chain and temperature. Both increasing temperature andincreasing side chain length are observed to decrease density. Trendssimilar to 1-n-alkylimidazoles are also observed for families of[C_(n)mim][X] ILs (e. g. , [C₂mim][BF₄], [C₄mim][BF₄], [C₆mim][BF₄]),however IL density is also strongly influenced by the nature of theanion, across a family with identical cations such as [C₄mim][BF₄],[C₄mim][PF₆], [C₄mim][OTf], etc. While densities of 1-n-alkylimidazoleswere observed to only vary about 15% between the least and most densespecies at a given temperature, densities of ILs can vary more widely.For example, a 30% difference is observed in the densities of[C₄mim][Tf₂N] (r=1.44 g/cm³) and [C₄mim][dca] (r=1.06 g/cm³) at 298 K.Even greater spreads are possible with smaller cations such as [C₂mim]or anions with greater fluorination such asbis(perfluoroethylsulfonyl)imide ([beti]). All [C_(n)mim][X] ILs areabout 10% or more dense than their 1-n-alkylimidazole analogues at thesame temperature.

The differences in densities between 1-n-alkylimidazoles and[C_(n)mim][X] ILs might influence certain process design considerations(e.g., head pressure in a vessel, increased mass flow rate), themagnitude of the difference (10-50%) is relatively small and withinrange of many common organic compounds. Common chlorinated organicsolvents (e.g., chloroform) are nearly as dense as the most dense ILs,while brominated compounds (e.g., bromoform) can be at least twice asdense as most [C_(n)mim][X] ILs.

While the change in density associated with transitioning from a neutral1-n-alkylimidazole to a [C_(n)mim][X] IL is relatively small, a penaltyis exacted on the solvent viscosity. Viscosity increases by an order ofmagnitude or more when transitioning from the neutral 1-n-alkylimidazoleto the [C_(n)mim][X] IL. For 1-n-alkylimidazoles, viscosity was observedto increase with increasing chain length and decreasing temperature. Asimilar trend holds for across a family of [C_(n)mim] ILs with the sameanion, [X]. However, viscosity differences between ILs with the same[C_(n)mim] cation and different anion species can be quite large,spanning almost an order of magnitude.

Example 6 1-N-Alkylimidazoles as Co-solvents for Post-Combustion CO₂Capture

In order to determine if 1-n-alkylimidazoles could be used assolvents/agents for low pressure CO₂ capture applications, the uptake ofCO₂ in an mixture of 1-butylimidazole (37.37 g, 158.2 mmol) andmonoethanolamine (MEA) (9.968 g, 163.2 mmol) (overall mixture about80:20 vol/vol) was determined using the same apparatus as described inExample 4, and a slightly modified experimental procedure. Initially, astream of CO₂ at about 1000 torr of CO₂ was fed to the cell for severalminutes. The valve was then closed and the pressure in the cell wasobserved to decay until an equilibrium pressure of 606 torr wasachieved. After obtaining the mass of the cell and applying Eqn. 1, itwas found that 118 mmol (5.20 g) of CO₂ were absorbed by the liquidphase.

An initial attempt to determine the exact reaction mechanism(s)responsible for the excess absorption of CO₂ was carried out using ¹HNMR spectroscopy. ¹H NMR spectra were obtained in d⁶-DMSO as well aswith no deuterated solvent. Proton signals originally in the range of6.0-6.5 ppm when the solvent had absorbed less than 100% of itstheoretical capacity were observed to shift downfield to the range of6.5-7.0 ppm when the solvent had absorbed more than 100% of itstheoretical CO₂ capacity. The chemical shifts were also furtherdownfield than were reported when CO₂ was captured by MEA in an[C₆mim][Tf₂N], which was limited to 0.50 mol CO₂/mol MEA due toprecipitation of the MEA-carbamate product. For the 1-butylimidazole-MEAsolvent mixture, a broad peak was observed even further downfieldbetween 8.5-8.75 ppm, when no deuterated solvent was included in the NMRsample, which is likely indicative of H⁺exchange between1-butylimidazole and MEA. These data indicate that 1-butylimidazole canhave a participatory role in chemical reactions to capture CO₂ in thepresence of an amine.

The viscosity of the CO₂-rich solvent was measured immediately after theexperiment was completed and the liquid phase rapidly transferred to theviscometer. The viscosity of the CO₂-rich solution was initiallymeasured as about 100 cP at 25° C., though the value drifted lower to 85cP over several minutes, presumably due to loss of CO₂ from the reactionproduct(s).

The results for the 1-butylimidazole-MEA mixture indicate that themixtures of 1-n-alkylimidazoles can be used as effective solvents/agentsfor low pressure CO₂ capture that provide high CO₂ capacity andrelatively low viscosities for the CO₂-rich phase, especially whencompared to TSIL compounds. Carbamate-imidazolium salt products can beconsidered as a type of reversible IL that exists as a product formedbetween CO₂, an amine and a 1-n-alkylimidazole.

Example 7 CO₂ and CH₄ Solubility Measurements

Solubilities of CO₂ and CH₄ in 1-n-alkylimidazoles were measured asdescribed above in Example 2. Experiments were conducted at temperaturesof 30, 45, 60, and 75° C. (as controlled by an oil bath) for both CO₂and CH₄ measurements. An initial charge of gas was fed at 30° C. untilthe pressure equilibrated at about 5 atm, which was selected as thetarget pressure. Solubility values for all temperatures were thencalculated from this known mass of gas in the system and the change inpressure upon heating (see, e.g., Finotello et al., “Room-temperatureionic liquids: Temperature dependence of gas solubility selectivity,”Ind. Eng. Chem. Res., 47:3453-3459 (2008), which is incorporated hereinfor its teaching of gas solubility measurements and calculations). Thevapor pressure of the 1-n-alkylimidazole compound can be assumed asnegligible under the experimental temperature and pressure conditions,as it is low (about 5 mmHg maximum and typically <1 Torr) and very small(about 0.1%) compared to the partial pressure of the gas (see, e.g.,Emel'yanenko et al., “Building Blocks for ionic liquids: Vapor pressuresand vaporization enthalpies of 1-(n-alkyl)-imidazoles,” J. Chem.Thermodyn., 43:1500-1505 (2011); Verevkin et al., “Thermodynamics ofIonic Liquids Precursors: 1-Methylimidazole,” J. Phys. Chem. B,115:4404-4411 (2011)). The respective errors associated with Henry'sConstants (H) and volumetric solubility (S) were calculated based uponpropagation of error of the experimental parameters (i.e., pressure,temperature, volumes, mass, etc.), in which all errors associated withthe instrumentation were quantified. In this method, both the moles ofgas dissolved in the liquid and the molecular weight of the gas arefactors to consider in determining the magnitude of the uncertainty. AsCO₂ is both more soluble and of a greater molecular weight than CH₄,measurements for CO₂ exhibit an order of magnitude smaller error thanthose for CH₄, with typical experimental errors of 1-2 and 10-15%,respectively. The errors for CO₂ solubility are consistent with thosedescribed above.

Henry's constants (H_(j) (atm)) and volumetric solubilities (S_(j)) ofCO₂ and CH₄ in 1-n-alkylimidazoles at temperatures between 30 and 75° C.are presented in Table 4.

TABLE 4 CO₂ CH₄ 1-n-alkyl- H_(CO2) H_(CH4) imidazole Temp (atm) ±^(a)S_(CO2) ^(b) ±^(a) (atm) ±^(a) S_(CH4) ^(b) ±^(a) 1 - Methyl 30 121 22.45 0.04 1920 270 0.14 0.02 45 180 3 1.61 0.03 2140 300 0.13 0.02 60221 4 1.24 0.02 2300 340 0.12 0.02 75 254 5 1.08 0.02 2420 380 0.11 0.022 - Ethyl 30 114 1 2.14 0.03 1240 150 0.19 0.02 45 153 2 1.52 0.02 1470210 0.16 0.02 60 180 3 1.24 0.02 1630 240 0.14 0.02 75 201 3 1.12 0.021760 280 0.13 0.02 3 - Butyl 30 86.3 0.9 2.07 0.03 584 39 0.27 0.02 45123 1 1.45 0.02 616 42 0.25 0.02 60 150 2 1.15 0.02 638 43 0.24 0.02 75170 2 1.01 0.02 656 43 0.23 0.02 4 - Hexyl 30 69.8 0.7 2.08 0.03 462 270.30 0.02 45 98.3 1.1 1.46 0.02 511 32 0.26 0.02 60 118 2 1.16 0.02 54535 0.24 0.02 75 134 2 1.02 0.02 572 37 0.23 0.02 5 - Octyl 30 68.3 1.01.78 0.02 571 57 0.20 0.02 45 91.5 1.0 1.32 0.02 704 79 0.16 0.02 60 1081 1.09 0.01 798 99 0.14 0.02 75 121 1 0.96 0.01 871 118 0.13 0.02 6 -Decyl 30 63.3 1.0 1.61 0.03 501 55 0.19 0.02 45 91.3 1.6 1.14 0.02 62477 0.16 0.02 60 111 2 0.90 0.02 712 100 0.14 0.02 75 127 3 0.77 0.02 779120 0.12 0.02 ^(a)Error represents one standard deviation. ^(b)S[=] (cm³gas (STP)) (cm³ solvent)⁻¹ atm⁻¹.

Table 4 reveals that, at any given temperature, 1-methylimidazoleexhibited the highest solubility of CO₂ and lowest solubility of CH₄ pervolume. 1-Hexylimidazole displayed the greatest volumetric solubility ofCH₄ under the same conditions. The solubility of both gases in each ofthe 1-n-alkylimidazoles decreased with increasing temperature. As apoint of reference, molar solubility data are also presented in Table 1as Henry's constants, and indicate that CO₂ is most soluble in1-octylimidazole and 1-decylimidazole, while still indicating that CH₄is most soluble in 1-hexylimidazole. However, the greater CO₂ solubilityindicated by the smaller Henry's constants for larger1-n-alkylimidazoles is primarily due to the >2 times increase inmolecular weight between 1-methylimidazole and 1-octylimidazole (i.e.,larger molar volume). Thus, the volumetric solubility data are useful informing direct comparisons to conventional solvents, ILs, and polymers(Bara et al., “Guide to CO₂ Separations in Imidazolium-BasedRoom-Temperature Ionic Liquids,” Ind. Eng. Chem. Res., 48:2739-2751(2009); Lin et al., “Materials selection guidelines for membranes thatremove CO₂ from gas mixtures,” J. Mol. Struct., 739:57-74 (2005)).

The solubility data in Table 4 indicate that 1-methylimidazole also hasthe greatest working capacity of the 1-n-alkylimidazole solvents interms of an absorption-regeneration process for CO₂ removal from CH₄using a physical solvent. The about 60% decrease in CO₂ solubilitybetween 30 and 75° C. indicates that CO₂ can easily be desorbed from thesolvent under moderate heating and/or mild vacuum.

With increasing chain lengths in 1-n-alkylimidazoles, it was observedthat CH₄ solubility (SCH₄) increased from 1-methylimidazole to1-hexylimidazole, yet declined in 1-octylimidazole and 1-decylimidazole.Although the overall solvent environments are much less polar in1-octylimidazole and 1-decylimidazole than in 1-ethylimidazole, thesesolvents exhibit similar levels of CH₄ uptake. These trends indicatethat greater hydrocarbon content does not necessarily favor CH₄dissolution in this family of molecules, as increasing chain length musteventually limit the available space for CH₄ to dissolve.

Example 8 Comparison of 1-methylimidazole to Commercial Physical SolventProcesses and Ionic Liquids

A general principle applied to selecting solvents for acid gas removalis that polar groups (ethers, nitriles, etc.) favor CO₂ dissolution andCO₂/CH₄ separation (see Bara et al., “Guide to CO₂ Separations inImidazolium-Based Room-Temperature Ionic Liquids,” Ind. Eng. Chem. Res.,48:2739-2751 (2009); Lin et al., “Materials selection guidelines formembranes that remove CO₂ from gas mixtures,” J. Mol. Struct., 739:57-74 (2005)). Thus, polar organic solvents (e.g., DMPEG, MeOH, etc.)are typically used for natural gas sweetening and other acid gas removalapplications. However, a variety of factors are considered for aphysical solvent to be used in a commercially viable process, includinglow volatility, low viscosity, stability, and availability in bulk atfavorable costs. Furthermore, no one physical solvent is appropriate forevery gas treating application, due to the differences in the gasstreams to be treated and/or the requisite purity of the product gas.Four of the most utilized physical solvents are dimethyl ethers ofpoly(ethylene glycol) (DMPEG), propylene carbonate (PC),N-methyl-2-pyrrolidone (NMP), and methanol (MeOH), each with its owncapabilities and limitations. A number of factors relating to solventproperties and the composition of the gas to be treated also play rolesin determining solvent selection.

For example, DMPEG is effective at achieving selective separation of H₂Sfrom CO₂, but has a higher viscosity than other physical solvents, whichreduces mass transfer rates, especially if operated below 25° C. PC isnot typically recommended for use when high concentrations of H₂S arepresent, as it becomes unstable during regeneration (about 93° C.). Ofthe solvents considered here, NMP has the highest selectivity forH₂S/CO₂, but is more volatile than DMPEG or PC. At ambient conditions,MeOH is quite volatile, but when chilled to subzero temperatures (as lowas about −70.5° C.), MeOH becomes effective at near complete removal ofCO₂, H₂S, and other contaminants. Chilling MeOH (or any physicalsolvent) increases acid gas loadings, but does so at the cost of thepower supply for refrigeration and potential increases in solventviscosity. However, these operating expenses can be offset via reducedsolvent circulation rates (process footprint), which results in lowercapital expenses. Also, as the solubility of CH₄ changes much less withtemperature than does CO₂ (or other acid gases), selectivityenhancements can be achieved through chilling. While CO₂ and H₂S aretypically the impurities present in the greatest proportions, otherminor species such as carbonyl sulfide (COS), carbon disulfide (CS₂),and mercaptans (RSH) can also be removed. Another consideration insolvent selection and process design is the absorption and loss oflarger hydrocarbons, which can accumulate in the solvent. Thus, processdesigns can be quite different for each of these solvents depending onboth solvent physical properties and the number of unit operationsrequired.

Table 5 presents the physical properties most relevant to processoperation for the four physical solvents discussed, as well as1-methylimidazole. Ionic liquids (ILs) have also been included in thiscomparison. All physical properties are at 25° C., unless otherwisenoted.

TABLE 5 1-methyl- DMPEG PC NMP MeOH imidazole Ionic liquids Viscosity(cP) 5.8 3.0 1.65 0.6 1.77  ~25-1000 Specific gravity (kg m⁻³) 1030 11951027 785 1031 1000-1500 Molecular weight (g mol⁻¹) 280 102 99 32 82~200-500  Vapor pressure (mmHg) 0.00073 0.085 0.40 125 0.37 0.000001Freezing point −28 −48 −24 −92 −6 Variable Boiling point (760 mmHg) 275240 202 65 198 N/A Max. operating temp. (° C.) 175 65 bp bp bp^(b)Depends^(a) CO₂ solubility (ft³ U.S. gal⁻¹) 0.485 0.455 0.477 0.4250.377 ≧0.335 CO₂/CH₄ 15 26 14 20^(c)  >17  8-18 H₂S/CO₂ 8.82 3.29 10.27.06^(c) ≧NMP^(b) 2-4 H₂O miscible? Yes Partial Yes Yes Yes Varies “bp”= boiling point; ^(a)Property depends on stability; ^(b)Estimated value;^(c)Solubility selectivity data at −25° C. for MeOH.

Table 5 illustrates that 1-methylimidazole is most similar to NMP interms of physical properties. Both NMP and 1-methylimidazole are about50% less viscous than PC and about 70% less viscous than DMPEG. While1-methylimidazole has about 20% lower CO₂ solubility than NMP and DMPEG,it has a higher CO₂/CH₄ selectivity than DMPEG and NMP. The potentialfor higher H₂S/CO₂ selectivity also exists in 1-methylimidazole based onanalogy to the CO₂/CH₄ and H₂S/CO₂ ratios observed for NMP, and thepresence of a basic, nitrogen center which has allowed its use as anacid scavenger, and should allow reversible acid-base interactions withthe acidic proton(s) of H₂S. Table 5 demonstrates that 1-methylimidazoleis useful for IGCC or pre-combustion CO₂ capture based on itsselectivity for H₂S/CO₂.

Example 9 CO₂ Capture by Imidazoles and Amines

The utility of imidazoles for CO₂ capture applications was examined bystudying mixtures of 1-butylimidazole with other amine-based compounds,including NMEA, API, AMP, piperazine, imidazole, and DIPA. Experimentswere carried out, as described above and in Shannon et al., “Propertiesof alkylimidazoles as solvents for CO₂ capture and comparisons toimidazolium-based ionic liquids,” Ind. Eng. Chem. Res., 50:8665-8677(2011), at ambient temperature (25° C.) and at CO₂ partial pressuresbetween 5-225 kPa. The relationships between CO₂ absorbed and pressurefor various 1-butylimidazole+amine combinations are presented in FIG. 2.

With the exception of 1-butylimidazole+imidazole, all combinationsexhibited chemical reactions with CO₂ as evidenced by a sharp increasein loading of CO₂ at partial pressures about 10 kPa. In the case ofpiperazine, which was only sparingly soluble in 1-butylimidazole, highlevels of CO₂ uptake were still achieved via rapid reaction of CO₂ withthe well-mixed slurry. Piperazine was nearly stoichiometricallysaturated with CO₂ in a 1:1 ratio prior to any appreciable pressuremeasurement could be obtained from the equipment. The slope of the linepresented (nearly parallel to that of the mixture containing imidazole,which experienced no chemical reaction at all) is thus indicative of CO₂physical solubility in 1-butylimidazole, as all of the piperazine hasalready been reacted with CO₂.

At loadings below about 0.35 mol CO₂/mol amine, 2-amino-2-methylpropanol(AMP) remained soluble in 1-butylimidazole and displayed a sharpincrease in CO₂ absorbed at partial pressures about 10 kPa. However,above this loading, AMP-carbamate precipitated from solution and therelationship between loading and pressure became more representative ofa physical solvent. Precipitation of AMP upon reaction with CO₂ iscommonly observed in organic solvents where carbamate formation isfavored, but not in aqueous solutions where carbonate formation is thepreferred mechanism.

NMEA did not precipitate from solution upon absorption of CO₂, andexhibited the most favorable loading profile. At a partial pressure of50 kPa, the 1-butylimidazole+NMEA mixture achieved a loading of 0.75 molCO₂/mol NMEA. In non-aqueous solvent containing 2° amines, it would beexpected that a level of 0.50 mol CO₂/mol amine could be achieved, withadditional physical solubility occurring at increasing pressure.However, physical solubility in the 1-butylimidazole solvent at theserelatively low CO₂ partial pressures could only account for a fraction(<20%) of the CO₂ absorbed in excess of the 0.50 mol CO₂/mol NMEAstoichiometric chemical reaction limit. By comparison of the slope ofthe data for 1-butylimidazolebimidazole, it appears that the combinationof 1-butylimidazole+NMEA creates a synergistic effect on CO₂ uptake.

DIPA, a bulky, hindered 2° amine also exhibited absorption behaviorsimilar to NMEA, but with less overall loading as the amine group isless accessible to CO₂ to form the carbamate.

Interestingly, API (an amine-imidazole hybrid) achieved a loading of0.50 mol CO₂/mol —NH₂ group below 10 kPa, yet exhibited only physicalsolubility for CO₂ at increasing pressures. Based on a possible H⁺transfer mechanism, this behavior indicates that the carbamate formedbetween 2 molecules of API is not accessible to 1-butylimidazole topromote levels of CO₂ uptake similar to solvents containing NMEA, or asin the case of AMP, 1° amines with bulky side groups are less likelycandidates to readily achieve loadings >0.50 per molecule of amine. Withthe exception of piperazine, which was a heterogeneous mixture, smallalkanolamines, such as NMEA and MEA, can achieve the greatest CO₂ uptakein imidazole-based solvents.

For NMEA, API, and DIPA viscosities of the CO₂-rich mixtures at themaximum CO₂ loading were measured immediately after the experiments werecompleted. The results are summarized in Table 6.

TABLE 6 Viscosity (cP) of CO₂-rich Compound Type solution (25° C.)N-methylethanolamine 2° alkanolamine 28-31 (NMEA) 1-(3-aminopropyl)-Imidazole - 1° 41 imidazole (API) amine hybrid DiisopropanolamineHindered 2° 27-32 (DIPA) alkanolamine

Interestingly, all of the CO₂-rich solvents had viscosities in the rangeof 30-10 cP, which represents an 8-10× increase from the viscosity ofneat 1-butylimidazole at 25° C. The 1-butylimidazole+NMEA viscosity inthe highly CO₂-rich state was only about⅓ that of a mixture containing1-butylimidazole+MEA at a similar loading. Although viscosity increaseswith CO₂ absorption, the values observed are still less than mostconventional ILs which cannot achieve high levels of CO₂ loading underthese partial pressures and other reactive & reversible ILs (see, e.g.,Bara et al., “Guide to CO₂ separations in imidazolium-basedroom-temperature ionic liquids,” Ind. Eng. Chem. Res., 48: 2739-2751(2009); Gardas et al., “A group contribution method for viscosityestimation of ionic liquids,” Fluid Phase Equilibr., 266: 195-201(2008)). Additionally, this viscosity range is approaching that of someaqueous amine solvents proposed for post-combustion CO₂ captureapplications as well as solutions already commercially applied in thenatural gas industry. Initial results indicate that further reductionsin viscosity can be achieved with N-functionalized imidazoles withshorten pendant alkyl chains (e.g., 1-methylimidazole,1,2-dimethylimidazole, etc.).

Based on the performance of the 1-butylimidazole+NMEA mixture at ambienttemperature, the temperature dependence of loading was characterized inorder to generate baseline data for both absorption and desorption inimidazolebamine mixtures. FIG. 3 presents these data across the range of25-80° C. at pressures >10 kPa. For typical flue gas conditions (40° C.,2 psia CO₂), the 1-butylimidazole+NMEA solvent achieves loadingsapproaching 0.50 mol CO₂/mol amine. As can be seen in FIG. 3, CO₂solubility decreases with increasing temperature for a given pressure.The 1-butylimidazole+NMEA mixture exhibits a working capacity ofabout0.40 mol CO₂/mol NMEA at a constant pressure when the temperatureis increased from 40° C. to 80° C. These data, combined with therelatively low viscosity in the CO₂-rich state, indicate thatimidazole+amine solvents are capable of both the capture and release ofCO₂ within a conventional absorber-stripper process.

As a wide variety of imidazole and amine derivatives might be used invarious concentrations to formulate solvent mixtures CO₂ capture, thisparticular combination of 1-butylimidazole+NMEA (80:20 vol:vol) is onlya representative example. Both the structures of the imidazole and aminecomponents are likely to influence both physical and chemical propertiesof the resultant solvent mixture.

Example 10 Imidazoles as Agents for SO₂ Removal

Alkylimidazoles can also be used to reversibly absorb SO₂ via bothphysical and chemical interactions. This feature presents interestingpossibilities as alkylimidazoles could be used as both a chemical andphysical solvent to recover SO₂ from flue gas.

To demonstrate absorption of SO₂ in an alkylimidazole solvent, anexperiment was carried out in a well-ventilated fume hood. A handheldSO₂ sensor was also employed to ensure exposure of personnel to SO₂ wasminimized. 1-Hexylimidazole (5.00 g, 32.8 mmol) was stirred in a 50 mLround bottom flask contained within a room-temperature water bath. Lowpressure SO₂ (about 1 psig) was bubbled into the solvent, and the totalsolution volume was observed to expand rapidly with a single liquidphase present. After 5 minutes of exposure to the bubbling SO₂ stream,the mass of the flask contents was observed to increase by 2.46 g,indicating that 38.4 mmol or 1.17 mol SO₂/mol 1-hexylimidazole werepresent in the flask. After the flow of the SO₂ stream ceased, thecontents of the flask were swept with a stream of N₂ for several hoursat room temperature. After this time, the liquid phase had transformedto a transparent, viscous gel, containing about0.5 mol SO₂/mol1-hexylimidazole as determined by the residual mass of the flaskcontents. The SO₂ lost is likely the portion that was physicallydissolved, thus indicating that SO₂ reacts with alkylimidazoles in a 1:2ratio. The chemically-bound SO₂ could be released by heating the sampleat >100° C. while under N₂ sweep. No irreversible degradation of the1-hexylimidazole was observed via ¹H NMR.

While 1-hexylimidazole was chosen for convenience of its very lowvolatility, this reaction could have been carried out with anyalkylimidazole compound. Thus, it is likely that the properties of thereaction product (i.e., viscosity and solid/liquid/gel state) betweenSO₂ and imidazoles will likely depend on the length of the alkyl chainas well as any additional functionalization at the C(2), C(4), and/orC(5) positions. Functionalization of the carbon positions can alsoprovide the ability to tune the equilibrium of the chemical reaction orcontrol desorption temperature.

As with the 1-butylimidazole+NMEA mixture for CO₂ capture, the exampleof 1-hexylimidazole is not optimized. However, N-functionalizedimidazoles present new opportunities for reversible SO₂ capture fromflue gas in the electric power industry. Reversible SO₂ capture is ofinterest as current “scrubbing” technologies rely on the reaction ofSO₂+CaSO₃ (CaSO₃, with CaSO₃ then oxidized to CaSO₄ and commonly soldfor use as drywall). Direct recovery of SO₂ eliminates processengineering issues with the handling of solids in flue gasdesulfurization, while simultaneously allowing for the production ofhigher value sulfur products such as H₂SO₄.

Additional opportunities exist in applying imidazoles for H₂S removalthrough an acid-base reaction similar to that exhibited by anhydrousamines. As the pKa of the first proton dissociation for H₂S is about7.0, 1,2-dialkylimidazoles and 1,2,4-triaklyimidazoles are capable ofnear quantitative deprotonation of H₂S to form an imidazolium bisulfidesalt.

The compounds and methods of the appended claims are not limited inscope by the specific compounds and methods described herein, which areintended as illustrations of a few aspects of the claims and anycompounds and methods that are functionally equivalent are within thescope of this disclosure. Various modifications of the compounds andmethods in addition to those shown and described herein are intended tofall within the scope of the appended claims. Further, while onlycertain representative compounds, methods, and aspects of thesecompounds and methods are specifically described, other compounds andmethods and combinations of various features of the compounds andmethods are intended to fall within the scope of the appended claims,even if not specifically recited. Thus a combination of steps, elements,components, or constituents can be explicitly mentioned herein; however,all other combinations of steps, elements, components, and constituentsare included, even though not explicitly stated.

What is claimed is:
 1. A method for removing a volatile compound from astream, comprising: contacting the stream with a solvent systemcomprising an N-functionalized imidazole, wherein the N-functionalizedimidazole is non-ionic under neutral conditions and is from about 20% toabout 80% by weight of the solvent system, and wherein the volatilecompound comprises carbon dioxide, carbon monoxide, sulfur dioxide,hydrogen sulfide, thiols, nitrogen oxide, nitrogen dioxide, carbonylsulfide, carbon disulfide, or any mixture thereof.
 2. The method ofclaim 1, wherein the N-functionalized imidazole comprises from about 30%to about 70% by weight of the solvent system.
 3. The method of claim 1,wherein the N-functionalized imidazole has the following structure:

wherein R¹ is substituted or unsubstituted C₁₋₂₀ alkyl, substituted orunsubstituted C₂₋₂₀ alkenyl, substituted or unsubstituted C₂₋₂₀ alkynyl,substituted or unsubstituted C₁₋₂₀ heteroalkyl, substituted orunsubstituted C₂₋₂₀ heteroalkenyl, substituted or unsubstituted C₂₋₂₀heteroalkynyl, substituted or unsubstituted cycloalkyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedthio, substituted or unsubstituted amino, substituted or unsubstitutedalkoxyl, substituted or unsubstituted aryloxyl, silyl, siloxyl, cyano,or nitro; and R², R³, and R⁴ are each independently selected fromhydrogen, halogen, hydroxyl, substituted or unsubstituted C₁₋₂₀ alkyl,substituted or unsubstituted C₂₋₂₀ alkenyl, substituted or unsubstitutedC₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀ heteroalkyl,substituted or unsubstituted C₂₋₂₀ heteroalkenyl, substituted orunsubstituted C₂₋₂₀ heteroalkynyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, substituted or unsubstituted heteroaryl,substituted or unsubstituted thio, substituted or unsubstituted alkoxyl,substituted or unsubstituted aryloxyl, substituted or unsubstitutedamino, cyano, or nitro.
 4. The method of claim 1, wherein the solventsystem further comprises an amine having the following structure:

wherein R¹, R², and R³ are each independently selected from the groupconsisting of hydrogen, substituted or unsubstituted C₁₋₂₀ alkyl,substituted or unsubstituted C₂₋₂₀ alkenyl, substituted or unsubstitutedC₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀ heteroalkyl,substituted or unsubstituted C₂₋₂₀ heteroalkenyl, substituted orunsubstituted C₂₋₂₀ heteroalkynyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, substituted or unsubstituted heteroaryl,substituted or unsubstituted thio, substituted or unsubstituted amino,substituted or unsubstituted alkoxyl, substituted or unsubstitutedaryloxyl, silyl, siloxyl, cyano, or nitro.
 5. The method of claim 4,wherein the amine is monoethanolamine, N-methylethanolamine,diglycolamine, diethanolamine, or N-methyldiethanolamine.
 6. The methodof claim 4, wherein the amine is 2-amino-2-methylpropanol.
 7. The methodof claim 4, wherein the amine is diisopropanolamine.
 8. The method ofclaim 4, wherein the amine is substituted or unsubstituted piperazine.9. The method of claim 4, wherein the N-functionalized imidazole and theamine are present in the solvent system in a weight ratio from 9:1 to1:9.
 10. The method of claim 1, wherein the stream is a natural gasstream, a synthesis gas, a liquid hydrocarbon stream, or a flue gasstream.
 11. The method of claim 1, further comprising regenerating thesolvent system by heating, applying vacuum or any combination thereof toregenerate the solvent system.
 12. The method of claim 1, wherein thesolvent system further comprises water.
 13. A solvent system forcapturing a volatile compound from a stream, comprising: from about 20%to about 80% by weight of an N-functionalized imidazole, wherein theN-functionalized imidazole is non-ionic under neutral conditions; and anamine.
 14. The solvent system of claim 13, wherein the N-functionalizedimidazole comprises from about 30% to about 70% by weight of the solventsystem.
 15. The solvent system of claim 13, wherein the N-functionalizedimidazole has the following structure:

wherein R¹ is substituted or unsubstituted C₁₋₂₀ alkyl, substituted orunsubstituted C₂₋₂₀ alkenyl, substituted or unsubstituted C₂₋₂₀ alkynyl,substituted or unsubstituted C₁₋₂₀ heteroalkyl, substituted orunsubstituted C₂₋₂₀ heteroalkenyl, substituted or unsubstituted C₂₋₂₀heteroalkynyl, substituted or unsubstituted cycloalkyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted aryl,substituted or unsubstituted heteroaryl, substituted or unsubstitutedthio, substituted or unsubstituted amino, substituted or unsubstitutedalkoxyl, substituted or unsubstituted aryloxyl, silyl, siloxyl, cyano,or nitro; and R², R³, and R⁴ are each independently selected fromhydrogen, halogen, hydroxyl, substituted or unsubstituted C₁₋₂₀ alkyl,substituted or unsubstituted C₂₋₂₀ alkenyl, substituted or unsubstitutedC₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀ heteroalkyl,substituted or unsubstituted C₂₋₂₀ heteroalkenyl, substituted orunsubstituted C₂₋₂₀ heteroalkynyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, substituted or unsubstituted heteroaryl,substituted or unsubstituted thio, substituted or unsubstituted alkoxyl,substituted or unsubstituted aryloxyl, substituted or unsubstitutedamino, cyano, or nitro.
 16. The solvent system of claim 13, wherein theamine has the following structure:

wherein R¹, R², and R³ are each independently selected from the groupconsisting of hydrogen, substituted or unsubstituted C₁₋₂₀ alkyl,substituted or unsubstituted C₂₋₂₀ alkenyl, substituted or unsubstitutedC₂₋₂₀ alkynyl, substituted or unsubstituted C₁₋₂₀ heteroalkyl,substituted or unsubstituted C₂₋₂₀ heteroalkenyl, substituted orunsubstituted C₂₋₂₀ heteroalkynyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, substituted or unsubstituted heteroaryl,substituted or unsubstituted thio, substituted or unsubstituted amino,substituted or unsubstituted alkoxyl, substituted or unsubstitutedaryloxyl, silyl, siloxyl, cyano, or nitro.
 17. The solvent system ofclaim 13, wherein the amine is monoethanolamine, N-methylethanolamine,diglycolamine, diethanolamine, or N-methyldiethanolamine.
 18. Thesolvent system of claim 13, wherein the amine is2-amino-2-methylpropanol.
 19. The solvent system of claim 13, whereinthe amine is diisopropanolamine.
 20. The solvent system of claim 13,wherein the amine is substituted or unsubstituted piperazine.
 21. Thesolvent system of claim 13, wherein the N-functionalized imidazole andthe amine are present in the solvent system in a weight ratio from 9:1to 1:9.
 22. The solvent system of claim 13, further comprising water.